Recently, a disk-shaped recording medium, such as an optical disc or a magneto-optical disc, utilizing the optical or magneto-optical signal recording/reproducing method, has been developed and presented to the market. As such disc-shaped recording medium, there are known a recording medium of the read-only-memory type (ROM) such as a so-called compact disc (CD), a so-called write once type recording medium on which data can be written only once by the user, and a so-called overwrite type disc, such as a magneto-optical disc, on which data re-recording is possible.
With a recording/reproducing apparatus for an optical disc, in which data are recorded or read out on or from the above mentioned write once type or overwrite type optical disc, the recording track on the optical disc is scanned by a light beam for data recording and/or reproduction, whilst the optical disc is rotationally driven at a constant angular velocity or at a constant linear velocity by spindle servo, and whilst focusing servo and/or tracking servo are supplied to an optical head on the basis of detection output of a photosensor adapted for sensing the light beam irradiated on and reflected back from the disc. The photosensor is enclosed within the optical head along with a laser diode which is driven by a laser driving circuit for outputting the light beam for data recording and/or reproduction.
With the recording/reproducing apparatus for an optical disc in which the recording track is scanned in this manner by the light beam for data recording and/or reproduction, if the power of the light beam scanning the recording track during the recording mode is too low, data cannot be recorded reliably, whereas, if the power of the light beam scanning the recording track during the reproducing mode is too high, serious effects may be produced, such as destruction of data recorded on the recording track. According to the Japanese Patent Kokai Publication No. 53-46633(1978), the intensity or volume of the light beam for data recording and/or reproduction is detected and the driving circuit for the laser diode adapted for outputting the laser beam is feedback controlled while a so-called APC servo loop for maintaining a constant beam power of the light beam is switched as a function of the prevailing operating modes for suitably switching the beam power.
Meanwhile, with an optical recording/reproducing apparatus in which the recording track is scanned by the light beam for recording and/or reproducing data on or from an optical recording medium, the light reflected from the optical recording medium is detected by an optical head, and the above mentioned focusing or tracking servo is performed on the basis of the resulting detection output. However, since the reflected light from the recording medium has been modulated by the pits formed on the recording track of the recording medium, that is, the recorded data, the operation of the servo system tends to be affected by the pits.
With the optical recording apparatus, the recording track on the optical recording medium is scanned by the recording light beam radiated by a laser diode driven by pulses in accordance with the record data during the recording mode, thereby forming the pits for data recording. However, inasmuch as a time delay .GAMMA. in the order of 300 to 400 ns is produced from the time when a recording light beam obtained by driving a laser diode by driving pulses consistent with the record data is irradiated until the pits P start actually to be formed, as shown in FIG. 1, the detection output waveform of the recording light beam reflected after irradiation on the recording track is also modulated with the above defined time delay. Thus the conventional servo system operating on the basis of the reflected light of the recording light beam exhibits a strong dependency on the pattern of the pits that is, the record data, formed on the recording track, so that it becomes necessary to provide a wide dynamic range automatic gain control circuit in the servo system.
Above all, in an optical recording/reproducing apparatus employing an optical recording medium having the modulation factor by the record data signal in the order of 60 percent, which is almost as high as that of the compact disc, such as a write once type optical disc having an organic dye optical recording medium, the problem is raised in connection with the effect on the operation of the servo system of the pit pattern formed on the recording track during the recording mode.
On the other hand, there is disclosed in the JP Patent Kokoku Publication No. 63-87656(1988) an optical disc in which a pre-groove formed thereon for tracking servo is wobbled as in the case of a so-called ATIP (absolute time in pregroove) and auxiliary data or sub-data, such as absolute time information, is recorded with the wobbling frequency component as the carrier wave. However, since the return light detected by the optical head during data recording has been affected with the time delay .GAMMA. as described above, the absolute time information cannot be reproduced satisfactorily. This is ascribable above all to the fact that indeterminate level components caused by reading the recorded pits give rise to generation of spectral components in the lower frequency range to lower the C/N ratio of the wobbling frequency to worsen the error rate during reproduction of the above mentioned absolute time data.
It is therefore an object of the present invention to provide an arrangement in which, even with an optical recording and/or reproducing apparatus in which an optical recording medium exhibiting a high modulation factor by the record data signal is used, error data of the focusing or tracking servo of the recording light beam or the wobbling time data may be detected reliably during the record mode operation to provide for a highly reliable recording operation. Thus the present invention provides an optical recording apparatus of a novel construction in which a light source for irradiating a light beam adapted for forming pits on an optical recording medium for data recording is driven by a reproducing level light volume during a time between successive data pulses for recording the data on the basis of control data obtained from the optical recording medium.